1. Field of the Invention
Example embodiments described herein relate to an exposure apparatus for manufacturing a semiconductor device. More particularly, example embodiments are directed to an off-axis illumination apparatus, an exposure apparatus, and an off-axis illumination method capable of varying an off-axis angle to a mask.
2. Description of Related Art
Generally, as the integration density of a semiconductor device increases, the dimensions of the device decrease. Various technologies have been developed for forming fine patterns on a wafer in a semiconductor exposure process, which are used in the manufacturing of semiconductor devices.
A pattern formed through the semiconductor exposure process may be obtained by irradiating light, for example, a laser, to a mask having a pattern so that the light transmitted through the mask may be irradiated to a wafer through an optical system.
However, in order to form the pattern having a fine line width on a wafer, a high optical resolution is generally required. However, the optical resolution may be difficult to obtain.
Accordingly, technology is continuously being developed to improve optical resolution of semiconductor manufacturing devices, which may be used for semiconductor exposure processes. A conventional example of one these technologies is to employ an exposure apparatus using an off-axis illumination method as opposed to an illumination method. The conventional off-axis illumination method may provide an optical resolution about 1.5 times greater than a conventional illumination method. Further, a depth of focus associated with a conventional off-axis illumination method is generally better than the depth of focus of a conventional illumination method.
In addition, a conventional exposure apparatus may use a modified aperture, wherein a light transmission region is annular or dipole, instead of circular. By using a conventional exposure apparatus having a modified aperture and an associated method, a vertical axis of light irradiated to the aperture may be blocked, and only an oblique component (e.g., off-axis component) may be transmitted through the aperture to irradiate a mask. In this case, the light passes through light transmission regions having various sizes of the respective apertures to form different off-axis angles (e.g., an angle between an optical axis of the off-axis component and a vertical axis irradiated to the mask) of the light irradiated to a mask.
Therefore, the off-axis angle irradiated on the mask may be determined according to the shape of the light transmission regions of the apertures and the transmissivity of light passing through the mask, which may also be varied. Therefore, when the off-axis angle is varied to adjust rear transmissivity of the mask, the aperture should be changed to another aperture. Accordingly, it may be difficult to obtain uniform exposure of a wafer considering the variable rear transmissivity because the off-axis angle irradiated to the mask cannot be adjusted and thus, a desired amount of light may not be provided onto the wafer. Therefore, exposure pattern failures may occur on the wafer, which may cause product failures.